Antenna



March 21, 1950 E. A. MARTINELL! ANTENNA Filed Aug. 1, 1945 INVENTOR.

ERA/ES 7' A. MART/NELL BY WA; 9 1642,

ATTORNEY i atenteoi li ter. 2i, 195t as War This inv tion rel tes to antennas for radio s and particular y to means anon pattern closely approxi- 2st: 0 in one plane, where 0 is the ed from the axis of the radiat ng mea s is a constant.

In certain airborne radio object-locating systems, for example, P. I. (plan position indieating) apparatus, it is des rable that the distrivertical plane throughout be such that the variation .s the radiation angle is a cosecant-squai- '-..nction. This provides rela-- tively constant echo strength for t rgets located on the earth or other surface regardless of whether the target is distant or c se in, and it eliminates the n of tilting the to ob tain adequate co: of th area unde' observation.

An object of the present on ion is to afford a cosecant-square adiation pattern the use of a modified al antenna. Another object is to achieve siirolicity in the design of such an antenna. Still other 1?. 'el features and advantages will be apparent f the following disclosure of the invention.

In the drawings:

Fig. l is a side elevation of an antenna embodying the invention;

Fig. 2 is a front elevation of the antenna;

Fig. is a 1: rspective View illustrating the development of the modified paraboloidal reflecting surface of the antenna; and

Fig. 4 is a p; ily diagrammatic View showing the manner in which the antenna may be mounts an -..e and the radiation pattern which it produces.

Referring to i and 2, radiating eiement or feed may be constructed and located in a conventional manner.

object-locating syfor obtaining r mating the r reflector ii 1 the present instance is formed in two parts. The lower portion iii extending below the level of the radiator iii, as viewed in Figs. 1 and 2, is a para boloidal surface having its focal point at the apparent center of radifon of he radiating source ill. The upper portion of the reflector M extending above the level of the radiator i2 is a modifi d parabclcidal surface, the configuration or which will described in detail herein-- after.

Fig. 4} illustrates the manner in which the antenna or 1 and 2 is mounted in the nose of an airplane i i so it scan the area disposed beneath the aircraft. The type of radiation pattern which is produced by this novel tineili, Arlington, Mass assignor, signinents, to the United States of represented by the Secretary of ioaticn [august 1, 1M5, Serial No. 663,294

antenna is indicated in broken lines and closely roxiinates the relation csc 0 where 0 is the radiation angle measured from the radiation axis 0-0. It will be appreciated that the P. P. I. type of scan which the present invention is particularly desi d is accomplished by rotation of the antenna about a vertical axis in a well- 1- shown surface along the parabola A-B-C. The ends or" this parabola are shown extended the broken li--es to intersect the latus rectum D E of the parabola. Now let it he assumed the parabola A-BC lying in the aforesaid plane passed through the focus F is rotated up- .vardly through substantially 98 about the latus rectum D--E as an axis, moving along the circular path indicated Fig. 3 to a position A'B- and thereby generating a barrel-like surface having a parabolic stave.

When viewed from the side, the modified paraboloidal surface has a configuration similar to that shown in Fig. 1 in which the lower portion i2 is parabolic and. the upper part it appears to lie along a circular are having center at the focal point of the paraboloid and with a radius through the middle of the reflector equal (to the nearest wavelength) to the focal length of the paraboloid. -i i hen viewed from the front, this surface appears as shown in in which the lower part iii l s a circular outline and the upper part it is parabolic. The upper portion oi the reflector it tends to concentrate the radiation d otly downward, while the lower portion 52 teids to concentrate the radiation ahead of the reflector. lhe combination of these efiects is such as to produce the csc 0 radiation pattern as described. It should be noted that modifications be made in the shape of the reflector ii, if desired, to alter the cosecantsquared pattern.

While 1 have illustrated and described a selected embodiment of my invention, it is apparent that variations and modifications may be made by persons skilled in the art without departing from the spirit of the invention. Hence I do not desire to limit the scope of the invention to the disclosed details but wish to avail myself of all improvements and modifications within the purview of the following claims.

I claim:

1. In an antenna for producing a cosecantsquared radiation pattern, a reflector comprising a portion having a paraboloidal reflecting surface and another contiguous portion having a barrelshaped reflecting surface with a parabolic stave.

2. In an antenna for producing a cosecantsquared radiation pattern, a reflector comprising, in combination, a portion having a reflecting surface shaped as a part of a paraboloid including the vertex thereof and disposed on one side of a ERNEST A. MARTINELLI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,735,377 Caughlan Nov. 12, 1929 2,061,508 Dallenbach Nov. 17, 1936 

